The invention relates to motor operators, such as for power switches of electrical utilities, and particularly to such operators for underground switches as well as switches in other locations, with a drive and control system that allows adjustment of motor travel settings resulting in the proper travel of the power switch.
Power switches, for example, disconnect and load break switches for distribution systems, are typically used in three main types of locations: overhead on a utility pole, in an underground vault, and pad mounted substantially at surface level. (Reference to “pad” or “pad mounted” herein, unless the context clearly indicates the contrary, is to be understood as mounted on an above ground pad.) It is of course the case that these switches can sometimes be mounted on a pad instead of being under ground. The switches can also be of different types. Unenclosed air break switches are often used on pole top installations. Enclosed, but not sealed, air break switches are often used at pad mounted installations. Enclosed and sealed switches, such as with vacuum or gas (e.g., SF6) insulation, are often used on or in locations, such as underground vaults, where the confined and sometimes flooded space makes air break switches inappropriate.
Switches in underground locations, and also in some pad installations, have motor operators located near the switches (in contrast, for example, to pole top air break switches that are mechanically coupled to motor operators on or near the ground). At one time power switches could be operated only by direct access to the switch or its operator. More recently, the power switch art has applied technology for remote, automated operation of a motor operator to close and open a power switch, (see, for example, Cleaveland/Price Bulletin DB-32BC04 (of 2004). During installation, however, the motor operator will need travel adjustment at the motor operator itself in order to operate the switch with the complete open or close position travel, which can be accomplished as disclosed in U.S. Pat. No. 7,122,986, issued on Oct. 17, 2006, to the present assignee, Cleaveland/Price Inc., said patent herein incorporated by reference in its entirety.
Extra danger to utility workers is encountered in tight locations such as underground vaults. For example, an enclosed switch may explode, due to heat buildup from arcing during a malfunction of the switch, subjecting workers to injury.
Motor operators for underground switch locations generally require a sealed enclosure to protect the operator from common flooding of the vault. For access to the interior of the enclosure for any reason, it has been necessary to have a port or panel of the enclosure that is removable and replaceable at the service location by a worker. In addition to the time needed to access the interior and to reseal the motor operator properly, perhaps dealing with up to thirty fasteners and a gasket, there is a risk the attempt to reseal is not successful and can lead to malfunction of the unit. The worker performing the field work is not equipped to test whether the seal is effective. Therefore, there is a need in the industry to adjust the travel of a sealed motor operator without disturbing the seal of the enclosure.
Generally, in the past, underground motor operators, required adjustment at the motor operator-power switch location to set the limits of travel of the motor in the motor operator which determine the travel limits of the power switch. This required accessing inside the sealed enclosure. For proper operation the motor drive unit (i.e., the motor itself and related gearing) needs to be able to move the power switch contacts to a definite closed position or a definite open position which requires adjustment of motor travel.
For final adjustment during installation and occasional readjustment over the life of the equipment, in the case of an underground switch, a worker would have to enter the vault where the switch and motor operator are located. Typically, limit switches to control the limits of travel of the motor operating shaft would need setting upon initial installation of the operator and switch and possible adjusting from time to time of the installation. The limit switches would have to be accessed by opening the enclosure containing the motor resulting in the risks mentioned above in the case of underground units, including at least at the risk to the integrity of the enclosure seal. While other locations, such as pad mounted at ground level, do not involve quite the same concerns for worker safety and motor operator integrity, the need for accessing the limit switches is at least an undesirable maintenance requirement.
Motor operators have been used or proposed having a switch actuator with a position-sensing feature between an output shaft of the motor of the operator and a lever that produces power switch opening and closing, for example, as in U.S. Pat. No. 5,552,647 issued to Ronald B. Tinkham on Sep. 3, 1996. Position sensing is shown by a potentiometer responsive to movement of a linear actuator to generate a signal indicating a position of a reference element on the actuator. The signal generated is communicated to control circuitry. The circuitry compares the signal to a standard to determine if the actuator travel is within limits determined by adjustable open-limit and closed-limit potentiometers. The arrangement is intended to improve on the prior limit switch assemblies which fail to provide sufficient accuracy and repeatability and tend to be complicated and costly. Such an actuator control is not one that avoids need for adjustment in the motor operator enclosure. The enclosure has an access hole specifically for adjustment of the open-limit potentiometer and the close-limit potentiometer. This adjustment requires a worker to enter the underground vault.
Other motor operators have been disclosed that also have a sensed position signal. U.S. Pat. No. 6,025,657, Feb. 15, 2000, is directed to a motor operator for either power on or manual operation without need for any decoupling or mode selection with a control system that receives signals indicating both the position of the drive output and the current drawn by the drive source. U.S. Pat. No. 6,215,263, Apr. 10, 2001, discloses a motor operator for overhead air break switches with a microcontroller subject to a variety of signals, including a position signal developed by a sensor that is a type of encoder. Some of the parameters relied on are temperature sensitive and require compensation. Some types of shaft position sensors, for example, including some encoders, depend on continuous power for a position signal to be reliably generated. Otherwise, after a power outage, the actual switch position would need to be observed and the motor travel limits reset. Such motor operators did not particularly address and respond to a need in the power switch art for avoiding needed travel limit adjustments in the enclosure of the motor, particularly important in underground sealed units.
As mentioned such motor operators will often need some adjustment at the motor operator itself in the case of a power switch having an open position and a dosed position, as disclosed in the aforesaid U.S. Pat. No. 7,122,986 B1. This patent discloses a power switch motor operator system which includes a first enclosure housing a motor with a motor shaft, a gear train running on the motor shaft, and an output shaft from the gear train having an end extending from the first enclosure to a movable contact of a power switch. A second enclosure is provided for containing a power supply and control assembly and a position switch panel that electrically communicates with the power supply and control assembly and includes switches for setting and adjusting travel limits for the motor shaft for the open switch position and the closed switch position using the signal from a potentiometer without requiring access to the first enclosure.
There has been a longstanding safety issue in the electric utility industry related to enclosed high voltage switch vaults and the need to operate the switch (without a person entering the vault) to a position which grounds the power circuit. The safest configuration for the vault mount switches is a GROUND position in addition to the OPEN and CLOSE positions. The GROUND position allows for the associated high voltage line to be grounded instead of merely open circuited. A grounded line assures the utility that any switching errors elsewhere on the system will not allow any voltage on the line that can injure or kill utility personnel. Additionally switch explosions in the vault caused by malfunctioning switch gear represent a fatal risk to any personnel in the vault. Currently in order to operate a power switch to the GROUND position requires electric utility personnel to enter the vault to perform the switching or the utility requires a complicated rope and pulley system to manually operate the switchgear to GROUND. Therefore it is an object of this invention to develop a power switch motor operator system that permits operation to and from the GROUND POSITION by remote electrical (non-manual) operation without the need for electric utility personnel to enter the vault or the need for a complicated rope and pulley system to manually operate the switchgear to GROUND.